1. Field of the Invention
The present invention relates to a novel salt and, more particularly, to a novel salt of 6-(4-bromo-2-chloro-phenylamino)-7-fluoro-3-methyl-3H-benzoimidazole-5-carboxylic acid (2-hydroxy-ethoxy)-amide (hereinafter referred to as “Compound 1”), which is a MEK inhibitor that is useful in the treatment and/or prophylaxis of proliferative disease states, such as cancer, in a mammal. More specifically, the present invention relates to a hydrogen sulfate salt of Compound 1 and to processes for the preparation of said salt. Also provided are pharmaceutical compositions containing a hydrogen sulfate salt of Compound 1, and the use of the salt in the manufacture of medicaments for treatment and/or prophylaxis of proliferative disease states, such as cancer, in the human or animal body, and methods of treating proliferative disease states, such as cancer, in a mammal by administering a therapeutically effective amount of a hydrogen sulfate salt of Compound 1.
2. Description of the State of the Art
Cell signaling through growth factor receptors and protein kinases is an important regulator of cell growth, proliferation and differentiation. In normal cell growth, growth factors, through receptor activation (i.e., PDGF or EGF and others), activate MAP kinase pathways. One of the most important and most well understood MAP kinase pathways involved in normal and uncontrolled cell growth is the Ras/Raf kinase pathway. Active GTP-bound Ras results in the activation and indirect phosphorylation of Raf kinase. Raf then phosphorylates MEK1 and 2 on two serine residues (S218 and S222 for MEK1 and S222 and S226 for MEK2) (Ahn et al., Methods in Enzymology, 2001, 332:417-431). Activated MEK then phosphorylates its only known substrates, the MAP kinases ERK1 and 2. ERK phosphorylation by MEK occurs on Y204 and T202 for ERK1 and Y185 and T183 for ERK2 (Ahn et al., Methods in Enzymology 2001, 332:417-431). Phosphorylated ERK dimerizes and then translocates to the nucleus where it accumulates (Khokhlatchev et al., Cell 1998, 93:605-615). In the nucleus, ERK is involved in several important cellular functions, including but not limited to nuclear transport, signal transduction, DNA repair, nucleosome assembly and translocation, and mRNA processing and translation (Ahn et al., Molecular Cell, 2000, 6:1343-1354). Overall, treatment of cells with growth factors leads to the activation of ERK1 and 2 which results in proliferation and, in some cases, differentiation (Lewis et al., Adv. Cancer Res. 1998, 74: 49-139).
In proliferative diseases, genetic mutations and/or overexpression of the growth factor receptors, downstream signaling proteins, or protein kinases involved in the ERK kinase pathway lead to uncontrolled cell proliferation and, eventually, tumor formation. For example, some cancers contain mutations which result in the continuous activation of this pathway due to continuous production of growth factors. Other mutations can lead to defects in the deactivation of the activated GTP-bound Ras complex, again resulting in activation of the MAP kinase pathway. Mutated, oncogenic forms of Ras are found in 50% of colon and >90% pancreatic cancers as well as many others types of cancers (Kohl et al., Science, 1993, 260:1834-1837). Recently, bRaf mutations have been identified in more than 60% of malignant melanoma (Davies, H., et al., Nature 2002, 417:949-954). These mutations in bRaf result in a constitutively active MAP kinase cascade. Studies of primary tumor samples and cell lines have also shown constitutive or overactivation of the MAP kinase pathway in cancers of pancreas, colon, lung, ovary and kidney (Hoshino, R., et al., Oncogene 1999, 18:813-822). Hence, there is a strong correlation between cancers and an overactive MAP kinase pathway resulting from genetic mutations.
As constitutive or overactivation of MAP kinase cascade plays a pivotal role in cell proliferation and differentiation, inhibition of this pathway is believed to be beneficial in hyperproliferative diseases. MEK is a key player in this pathway as it is downstream of Ras and Raf. Additionally, it is an attractive therapeutic target because the only known substrates for MEK phosphorylation are the MAP kinases, ERK1 and 2. Inhibition of MEK has been shown to have potential therapeutic benefit in several studies. For example, small molecule MEK inhibitors have been shown to inhibit human tumor growth in nude mouse xenografts, (Sebolt-Leopold et al., Nature-Medicine 1999, 5(7):810-816; Trachet et al., AACR Apr. 6-10, 2002, Poster #5426; Tecle, H., IBC 2nd International Conference of Protein Kinases, Sep. 9-10, 2002), block static allodynia in animals (WO 01/05390) and inhibit growth of acute myeloid leukemia cells (Milella et al., J. Clin. Invest. 2001, 108 (6):851-859).
Small molecule inhibitors of MEK have been disclosed. At least thirteen patent applications have appeared in the last several years: U.S. Pat. No. 5,525,625; WO 98/43960; WO 99/01421; WO 99/01426; WO 00/41505; WO 00/42002; WO 00/42003; WO 00/41994; WO 00/42022; WO 00/42029; WO 00/68201; WO 01/68619; and WO 02/06213.
Inhibitors of the MEK are also described in WO 03/077914. 6-(4-Bromo-2-chloro-phenylamino)-7-fluoro-3-methyl-3H-benzoimidazole-5-carboxylic acid (2-hydroxy-ethoxy)-amide, or “Compound 1”, is exemplified in WO 03/077914 and possesses the following structural formula:

Compound 1 has been shown to possess inhibitory activity against MEK and therefore to be useful in the treatment of a hyperproliferative disease such as cancer.
WO 03/077914 discloses, in general terms, certain pharmaceutically acceptable salts of the compounds disclosed therein. Specifically, it is stated in WO 03/077914 that pharmaceutically acceptable salts of the compounds disclosed therein that possess a sufficiently basic moiety may form acid addition salts containing pharmaceutically acceptable anions, and a range of such anions are listed. Similarly, suitable salts of the compounds possessing an acidic moiety are to be formed by treatment of a compound with a basic compound and particularly an inorganic base.
The form of a pharmaceutically active compound which is used in medicaments is suitably one that provides for reasonable handling properties, which allow it to be processed and formulated. However, it is also necessary to ensure that the biological properties of the final formulation, such as dissolution rate of tablets and bioavailability of active ingredient are optimized, and there is frequently compromises to be made in selecting a particular form which best fulfils all these various requirements. However, in some cases, salts do not form easily and/or are not stable, which is probably due to low pKa values. The pKa value expresses the strength of acids and base, i.e., the tendency for an acid to lose a proton or a base to add a proton (Bronsted J. N., Rec. Tray. Chim. (1923) 47:718). This is particularly true for Compound 1.